Why are the bioluminescent bays in Puerto Rico worth visiting?

Why are the bioluminescent bays in Puerto Rico worth visiting?

There is a handful of bioluminescent bays in the world, but the brightest ones are arguably in Puerto Rico.  The U.S. commonwealth of Puerto Rico has three “bio-bays”:

Almost all vendors charge $35 to $45 per person for each tour, lasting about 2 hours, depending on the season.  It is a little costly, but it is a worthy one-time expense.  Most vendors accept major credit cards and cash at the meeting point.

Mosquito Bay is the brightest and healthiest among the three locations but is only accessible by private plane (from Ceiba Airport or Isla Grande Airport) or by taking a one-hour ferry (~$2.25) from the Fajardo Ferry Terminal.  Note that it is not possible to visit Vieques and see the Mosquito Bay all in the same day if traveling by ferry.  As implicated in the name of the lagoon, you must remember to use mosquito repellent; they particularly like the blood of foreigners.

The brightness also owes in part to the significantly low level of light pollution on the island.  Mosquito Bay is the only bio-bay that still permits swimming, which is highly recommended.  The silhouette of your body is outlined by a band of neon-like glow as you move in the water at night.

La Laguna Grande (“Big Lagoon”) in northeast part of Fajardo is the second brightest and healtiest.  It is easily accessible by car and is a 1.5 hour drive from Old San Juan.  A good set of driving instructions are provided by Kayaking Puerto Rico, which is among the numerous providers of daily bio-bay excursions.  I picked Kayaking Puerto Rico among the crowd because it has an online reservation system and is rated “excellent” by 600+ reviewers on TripAdvisor.  All tours meet and depart from Las Croabas in Fajardo.  Due in part to the increasing number of vendors in recent years, current environmental laws prohibits swimming in the lagoon in order to protect the population of the delicate wildlife.

La Parguera is the dimmest bio-bay as the population of bioluminescent organisms there has been reduced significantly due to pollution and commercial activities.  However, it is great place for scuba diving and snorkeling.

What is bioluminescence?

Bioluminescence is an organism's ability to produce “cold-light” through a chemical reaction involving the oxidation of luciferin into photons using ATP energy with the help of luciferase enzymes.   Bioluminescence should not be confused with more commonly known fluorescence, which is hot-light emission resulting from the excitation of electrons.  For many marine organisms, emission is of blue and green light spectrum as these wavelengths can transmit through seawater most easily.

Some organisms use bioluminescence as a mechanism to camouflage (cookiecutter shark), to attract mates (fireflies), to illuminate (black dragonfish), to repulse (certain squid), or to communicate (bacteria).  Dinoflagellates make use of bioluminescence in a rather clever way.  They glow in response to the detection of motion by predators in the water.  However, it is not meant to frighten the enemy, but instead, it is intended to attracts even larger predators, which will consume the would-be predator of the dinoflagellate.  Think if it as a "burglar alarm" against one of their biggest threat, the krill.  One other unique aspect is that dinoflagellates are incapable to turning off their glow at will like fireflies can.  Once switched on, the glow stays for a preset time of a fraction of a second.

The largest occuring species of dinoflagellates, phytoplanktons, in the seawaters of Puerto Rico is Pyrodinium bahamense, which are unicellular protists (neither plant nor animal) measuring about 1/500th of an inch in diameter.  However, the instantaneously emited photon cloud is about one hundred times larger.  The result is a spectacular show of light for the human eyes that is best appreciated under a moonless night, or when the moon is at quarter stage.  Half-moon or full-moon conditions produce too much ambient light.

Why is the concentration of phytoplanktons so high?

Being harvesters of sunlight energy, phytoplanktons are dependent on light levels and nutrient availability for proliferation.  Puerto Rico's Mosquoito Bay (Vieques Island) and Grande Lagoon (Fajardo) are lagoons shielded from rough ocean currents and surrounded by Red Mangroves (Rhizophora mangle), which grow in the tropical and subtropical areas in both hemispheres. The roots of the red mangroves release biomolecules called tannins that are rich in Vitamin B12, one of the important nutrients for these primary producers of aquatic life.  The decomposing mangrove leaves release many other nutrients, which add to the nutrient rich estaurine ecosystem, making it an ideal breeding and nursing area.